Surface combustion process



ct. 5, 1937. 1- w, HAYS 2,095,065

SURFACE GOMBUSTION PROCESS Filed Jan. 25, 1935 3 Sheets-Sheet 1 v oct. 5, 1937. J w, HAYS 2,095,065

SURFACE COMBUSTION PROCES S Filed Jan. 25, 193s s sheets-sneet 2 Oct. 5, 1937. J, w HAYS 2,095,065

SURFACE COMBUSTION PROCES S Filed Jan. 25, 1935 3 Sheets-Sheet 3 Patented oa. s, 1931 UNITED STATES PATENT oFFlcE 2,095,065 summon coMBUs'noN rnocEss Joseph W. Hays, Tulsa, Okla.

Application January 25, 1933, Serial No. 653,469 1 claim.` (el. 15s-117.5)

The accompanying drawings and some of the written matter of the-present specification are the same as in my co-pendlng application, Serial Number 653,468 and of even date herewith, in`

5 which said application I disclose and claim the structural means by and' throlwh which the processes herein described and claimed are made possible and actually are accomplished.

My discovery relates particularly to all those l applications of gas, oil and other burners where combustible mixtures of air and gas or air and vapor, or air and a powdered combustible, are burned under pressure, whether high or low, and where it is desirable to mix the fluid, or suspended,

1J combustible and the air in the proper proportions before ignition. While my invention is designed primarily for the so-called "surface," or flameless combustion burners wherein the combustion takes place in a bed of refractory ma- 20 terial, whether said refractory material is packed in a tube or otherwise, and while all of my references and the drawings herewith relate to burners of the above type, I do not limit myself to them. My process can be advantageously employed in 25 all cases where thorough premixture is required prior to z ignition, regardless of the pressure, whether positive or negative, under which the combustion takes place. While I refer especially to gas fuel in this specification, I do not hold my- 30 self limited in any way to gas. My invention is applicable to vaporized oil, powdered fuel, or any other fuel which may be mixed with air ln any sort of combining proportion.

U. S. Patent No. 1,015,261 referring to Surface 35 combustion, as it is now known, was granted to W. A. Bone, of Leeds, England, on January 16, 1912, upon an application iiled December 3, 1910. This patent discloses an application of the process to steam boilers, water-heaters and the like. The

40 drawings show tubes packed with granular material, the inflow end of each tube being stopped with a plug through which there is a centrally located hole for the admission of the air-gas mixture. 'I'he outflow end of the tube was left 45 open,`except for a wire-mesh screen which was used to hold the pacldng material in place. Air under a pressure of 20 inches (water gauge) was used, and this, together with the gas with which it was mixed, was forced through the tube. 50 It will be seen very readily that the combustion capacity of a tube so equipped is limited by the inow tube and the pressure applied to the air-gas mixture. Dr. Bone states in his speciiication that he has burned 100 cubic feet of 560 55 B. t. u. coal gas per tube per hour at a pressure of 20 inches, water gauge, (about 11% ounces). By means of my invention I have been able to burn 165 cubic feet of 1050 B. t. u. gas per tube per hour at a pressure of 3*/2 ounces. I have burned 400 cubic feet per hour at a pressure of 5 8 ounces, and I have burned from 500 to 680 cubic feet per hour at a pressure of one pound. My invention enables me to obtain these extraordinary capacities because it does not restrict me to the use of an inow tube of small capacity. 10 On the contrary, I do not make use of an inow tube at all. The gas-air mixture is introduced into the open end of the combustion tube itself, the only restriction to the free ow of gas through the tube being that of the frictional resistance l5 of the refractory packing and the expansion of the gases in the hot combustion zone. The capacity limits of a combustion tube equipped with my invention are xed only by the pressure applied to the air-gas mixture and the ability of the refractory materials used to withstand high temperatures. I have used tubes ranging in diameter from 11/2 inches up to six and more inches.

'One object of my invention, therefore, is the attainment of high rates of combustion in surface combustion tubes; and another object is safety.

In the Bone patent, above referred to, reference is made to back-firing" in the tube leading from the mixing chamber, where the gas and air are commingled, to the tube in which the combustion takes place. This tendency has beenl oifset by Bone in various ways, viz.: (a) by making the inflow tube of such length and of such small diameter, and by giving the explosive mixtme such velocity through this small tube, that the velocity of flame propagation (velocity of vnashback) is exceeded,` (b) by admitting the air and gas separately until temperature has been established in the combustion tube, whereupon an air- 4o gas mixture is introduced from a mixing chamber; (c) by igniting at the rear, or outflow, end

of the combustion tube and relying upon the refractory packing to retard the tendency to backiire until temperature has been established; and (d) by increasing the pressure applied to the combustible mixture until a velocity is attained exceeding the velocity of ame propagation. As an insurance against disastrous explosions, Bone provides an explosion door" in the mixing chamber wall.

'Charles E. Lucke, in Patent 1,259,029, issued March 12, 1918, describes and claims a form of screen to prevent back-flashes. The same inventor, in Patent 1,313,196, claims another form of as a had feature of forced-draft surface combustion and have sought to obviate the consequences in various ways, but always either by devices for increasing the velocity of flow of the unignited mixture or by interrupting the progress of flame backwards through the mixture towardthe mixing chamber. In the specification cf Patent 1,259,029, previously referred to, the inventor states:

"Back-flash may be prevented by the cooling action of the walls of small or narrow through which the mixture is caused to flow, or by causing the mixture to approach thev sono with a velocity greater than the rate of propagation of inflammation.

This, so' far as my knowledge goes, s the state of the art prior to my invention.

For a number of years past I have experimented with surface combustion in tubes and in diaphragms, using coal gas, water gas, vaporised oil, natural gas and even coal. I have operated such tubes both with induced draft and with forced draft. When suction or induced draft is used to promote now through the the gas andairmaybedeliveredthroughcneor more nozzles, or pipes, directly against the cold surface of the refractory materials,lor the gas may be delivered separately and the air drawn inf' around the gas pipe or pipes, or vice versa. Ignition in either case is a very simple matter, as atorch ora match may beused. Themixture may be allowed to burn at ornear the surface of the refractory materials until the latter become heated for some distance below the surface. whereupon the gas may he turned oi! for a few moments, and, when turned on again, the gas will ignite and combustion will proceed entirely below or beyond the surface of the refractory materials. 'I'here can be no back-flash" in such cases.

I have found forced draft to he more emcient than induced draft in surface combustion tubes.

When induced draft is used there is a tendency toward short-circuiting, channeling, or "laning of the gases through the refractory bed, because of the negative pressure. But when the pressure is positive, as in the case of forced draft, the combustible mixture and the gaseous products of combustion are forced into all of the interstices of the packing. 'I'his results in a better combustion and a higher efficiency.

. Hitherto the objections to the use of forced draft in surface combustion tubes have been those relating to dangerous back-flashes and the diiiiculties of securing ignition. My invention makes it impossible for back-flashes to occur, regardless of the velocities of the gas and the air and the "rate of propagation of tion" of the mixture. ThisI believe, is new to the art and very highly useful, as it makes the internally fired surface combustion tube both safe and practicable. I have also discovered a practicable means of igniting the mixture-ln the-closed combustion tube, but this I am making the subject of a separate patent application.

The simplest and most obvious way of produc-- ing the desired mixture of air and gas where a fan is used to produce forced draft, is by introducing the gas with the air at the intake of the fan. The mixture in such case is necessarily thorough, regardless of air and gas ratios. The best results with surface combustion are attained when the mixture is at, or very close to, the chemical requirements and such a mixture is very easily attained by the method referred to, as it is necessary merely to increase the volume of gas delivered until the desired point is reached. But this method is subject to very serious hazards, especially if the explosive mixture is delivered from a common wind-box to a number of surface combustion tubes. A flash-back into such wind-box, or mixing chamber, would result in a terrific and perhaps destructive explosion. While I have prevented "flash-backs" by the use of screens and other devices I have always been obsessed by the. thought of what would happen if the screen, for any reason, should fail to` function. Assuming the use of 'a perfect anti-nashback screen, or other device, it is proper to consider what would happen if the explosive mixture in the wind-box", or mixing chamber, should be ignited by a spark or some cause other than that of a flash-back. The results vwould be precisely the same in the one case as in the other. p

There can be no explosion where no explosive mixture exists. I attain the principal object of my invention by mixing the gas and the air in the proper proportions at, or very close to. the

. point whereit is desirable to ignite the mixture, at which point, and beyond, combustion necessarily proceeds normally and continuously so long tions.

Reference may now be had to the accompanying drawings which illustrate the principles of my invention.

Figure 1 is a cross-sectional view of the mixing device without its housing, the latter, which carries the intake for the ain-being preferably, but not necessarily, an integral part of the tube, J, Figure 5. f

Figure 2 is an end view showing the gas supply tube tips and nozzles.

Figure 3 is a sectional view on the line, z-, Figure 1.

Figure 4 is a-detail of one of the tubes, N,*Fig ure 1.

Figure 5 is the complete assembly of combustion tube with its accessories and the mixing device, all shown in cross-section.

Figure 6 is an end view of the discharge end of the combustion tube showing the grid holding the refractory inthe tube. v Y

Figure 7 is a bottom plan view of the mixer and its accessories, together with the combustion tube and its accessories.

Figure 8 is an assembly view in side elevation, showing a mixer, combustion tube, etc., together with a pressure blower.

In Figure 1, P is a gas-supply pipe throughv which gas is preferably furnished under a pressure in excess of the operating pressure and in excess of the air pressure. Should the static pressure of the gas be less than that of the air no gas could iiow to the mixer.

On the otherI hand, the air, owing to its much greater volume.'

as the mixture is provided in the proper proporat common pressure to all of the tubes. N, but it is not a basic part of my invention. The tubes, N, are set gas-tight in the plate, TP, and the latter is secured by the bolts, L, to the flange of the detachable housing, DH, of the chamber, C. G is a gasket of any suitable material to make the chamber, C, gas-tight. V is a Venturi orifice plate with orifices, O, of the well-known Venturi type. The nozzles of the tubes, N, are aligned, as shown in the drawings, with the orifices, O. 'I'he adjustable spacers, S,are used to ilx the nozzles, Nl, of the tubes, N, at the desired distance from the orices, O. These spacers may be of any form to satisfy the requirements. In the drawings I show them as rods turned at each end to provide shoulders, one of the turned-down ends being threaded to screw into the plate, V, and the other passing through TP to which it is secured by the nut, Nt, as shown. W is a gasket of the washer type to prevent leakage of gas from C. St is an equalizer, or straightener. Its use will be explained later in this specification. Should it be desired to change the distances of the nozzles, Nl, from the orifices, O, the nuts, Nt, may be removed and the spacer-washers, SW, or some of them, shifted to the opposite side of TP, thereby bringing NZ into a closer or more distant position with respect to 0, as desired.

'I'he above letters and numerals are used throughout the several drawings.

The complete assembly of mixer and combustion tube is shown in the drawings, Figure 5, in which CT is the combustion tube and Re the refractory material with which the tube is packed. Gr is a casting, in the form of a grid, which serves to retain the refractory material in the tube while providing sufilcient space for the escape of the waste gases. Gr may be secured in place by any practicable-means. J is a jacketing tube surrounding CT and spaced apart therefrom at any desired distance. Flat metal rings, R, are welded to J and CT so that the space between the two tubes, (Sp), is completely enclosed, except for the inlet pipe, In, and the outlet pipe, Ot. The fluid to be heated, Fd, whether water, oil, vapor or any iiuid or liquid, is caused to ilow through Sp, preferably, as shown, in a direction contrary to the flow of the hot gases, through CT.

In the preferred form of construction, which isshown in the drawings, the tube, J, extends a short distance beyond one end of CT and forms a housing, H, for the mixer, illustrated in Figures 1, 2, 3 and 4. Fl is a flange which is welded to J and at the extreme end thereof. Fl is provided with bolt-holes, corresponding to those in F and TP, and Gl is a gasket to render the mixer, M, air-tight. Air under the desired pressure,Y

whether in ounces or in pounds, is admitted to M through the inlet, A. ID is an igniting device, which may be a spark plug. as shown, or any other suitable contrivance.

My invention will be best understood if I next explain the method of its operation.

Air in suillclent volume and at the desired pressure may be supplied by a suitable blower, a compressor or in any other manner. I prefer a pressure-volume blower, PB, which is indicated in Figure 8. Whatever means may be employed to provide a flow of air,'it is highly desirable that the air be delivered in constant volume and at constant pressure.

Gas is delivered through the pipe, P, at a pressure which should be constant and preferably in excess of that at which the air is supplied.

'I'he higher the gas pressure the better for the following reasons:

1. In order to secure the best possible distribution of the gas and the best possible air-gas mixture, I prefer to deliver the gas through a multiplicity of nozzles, Nl. I have found that the best results are secured when the orifices or vents of these nozzles do not exceed ,11nd or /Mths of an inch in diameter. Such small 'openings under low pressure operation might become clogged with dust or other foreign material carried by vthe gases, but if the latter are under a considerable pressure head this will be less likely to happen.

2. The higher the pressure of the gases the greater the velocity of the air-gas mixture flowing through the orifices, O, and, likewise, the greater the mushrooming eiect when the mixture impinges upon the refractories, Re. Such mushrooming, or spreading, promotes a thoroughness of air-gas mixture.

3. Gas for industrial uses can usually be secured at high pressures without increase of cost. Pressure gas, therefore, represents an available amount of kinetic energy, costing nothing, and this should be utilized whenever possible. High pressure gas reduces the load on the air blower and thereby lowers the cost of operation.

It will be understood that the drawings are illustrative, and the number and spacing of tubes N or orifices O can be varied as desired.

Air is delivered to the chamber, M, through the inlet, A. 'I'he air circulates in the space between the housing, H, and the nozzle tubes, N,

and from this space enters the tubebank from all sides. To avoid turbulence at, and an unequal distribution of air to, the numerous nozzles, the straightener, St,- is used to'straighten the air flow and break it up into a series of currents running parallel with the tubes, N, which are severally aligned with the oriiices, O. St serves to equalize the distribution of the air and air pressure and prevent short-circuiting to the nearest orifices. St is merely an orifice plate with holes in alignment withl the orices, O. It is adjustable as to position by means of the spacers, Sl, which are washers of various thicknesses, and the space desired may be arrived at by increasing or decreasing the number of washers. I find, in practice, that very satisfactory results are se cured by positioning the straightener approximately as shown in my drawings. The straightener may be considered as a desirable accessory, but by no means a basic part of my invention.

'I'he air and gas are mixed in the orifices, O. The gas, being under relatively high pressure, is projected at high velocity and in a diverging cone into each orifice, drawing air with it from the surrounding stream of air. 'I'he air, being under pressure, flows under its own velocity head into the gas stream. 'I'he velocity in the orifice is, therefore, a composite of the velocities of the air and the gas, and this velocity is accentuated by the Venturi effect of the orifice. Mixture is completed to a point of extreme thoroughness because of the multiplicity of the gas-air streams, and because of the mushrooming effect when these streams impinge upon the broken surfaces of the refractory materials, Re. The gases are ignited in the vicinity of this point of impingement by means of an ordinary spark-plug, or other igniting device, ID. It .will be seen that a flash-back is impossible for the reason that the point of ignition lies in, or near to, the very locality where the gas and the air are brought together to fonn a combustible mixture. There is no reason for a screen or other anti-flashback device, because there` can be no hash-back into ture is reached, the heat being produced, very` largely if not entirely, in the radiant form. Combustion is practically instantaneous. This being so, the capacity limits of such a combustion tube are ilxed by the free area ofthe interstitial spaces of the refractory packing and by the pressures used to force the gases into and through the tube.

The combustion zone, or hot-spot, is indi- 'cated in Figure 5 by the dotted lines, CZ. VThe transfer of'heat from the incandescent refractories, Be, in CZ to and through the tube, CT,

to the fluid, Fl, is almost instantaneous, the heat being in the radiant form. CT may be packed with the refractories, Ita-throughout itsentire length-if considered advisable. The hot gases vleaving CZ are "bailled" Vbyetheserefractcries and brought into: contact repeatedly with CT, `giving up their heat as they flow. Furthermore, these gases heat the refractories themselves and the heat is transferred by radiation and conduction from onegrefractory element of the packing to another and nally to the tube, CT, through which 7it is conveyed to the fluid in the space, Sp. In this waya very rapid and very complete transfer ofheat is effected.

The'positi'oning of the combustion zone, CZ, is a very important consideration in all cases where lauch combustion tubes are employed. The advantages of counter-flow in eil'ecting heat exchanges are well known. The iluld to be heated should, in all cases where possible, ilow in a direction contrary to that of the hot gases. This is best accomplished, as in the present instance, by ilxing the location of the combustion zone at theextreme end of the combustion tube, C'I, and approximately adjacent to the place where the heated fluid reaches its outlet. In this way the fluid, when in its hottest state, is exposed to the highest temperature and, when in its coolest state, on entering the heater, is exposed to the lowest temperature. capacities and eillciencies are obtained.

vdo not hold myself as limited to tubes.

Thus the highest heater It can easily be seen that if the combustion zone should be established at the opposite end of the combustion tube, or midway of the tube, there would be a marked loss of heat energy with the waste combustion gases, and this would be reflected adversely -upon the heating device, both as to its em'ciency and its capacity.

Previous inventors, as 'already explained, have ignitedvthe air-gas mixture at the discharge outlet of thel combustion tube, relying upon a -balancing of the velocities of mixture ilow and of flame propagation to ilx the location of the combustion zone, but I have found that the combustion zone is likely to remain fixed at, or close to. the spot where it is ilrst established. 'Ihe tendency of the hot-spot to remain stationary is influenced to some extent by the state of the refractcry packing, as to coarseness or ilneness, by

' the length of thetube and by the temperatures attained in the "hot-spot" as well as by the velocities. There is an enormous increasein gas flowV of the gases through the tube.

My invention enables me, among other things,

` to ilx the combustion zone at the forward end of the combustion tube, or yat any other point where I may prefer to ignite the mixture, and to maintain said zone substantially in its original location and position.

While I have shown tubes in my drawings and referred to them as such in this specification, I Any form of chamber or receptacle may be used to hold the refractory materials or the fluid which is .to be heated, whether that form be tubular cr otherwise, as it is plain that I can vary the size, shape and materials of any and al1 of the structures shown and claimed without departing from the spirit of my invention.

I claimz- The process of surface combustion of explosive mixtures of air and combustible iluid fuel freely miscible with air which comprises discharging the fuel in jets, discharging air in streams around said Jets to mix with the fuel, impinging the fuel and air while partially mixed upon a fixed' porous body, spreading the partially mixed air and fuel over the surface of said body to complete mixture of the fuel and air, then flowing the completed mixture through the pores in said body and burning the mixture in said body.

JOSEPH W. HAYS. 

